(CNN) -- Death already has a surprisingly vivid presence online. Social media sites are full of improvised memorials and outpourings of grief for loved ones, along with the unintentional mementos the departed leave behind in comments, photo streams and blog posts.

Now technology is changing death again, with tools that let you get in one last goodbye after your demise, or even more extensive communications from beyond the grave.

People have long left letters for loved ones (and the rare nemesis) with estate lawyers to be delivered after death. But a new crop of startups will handle sending prewritten e-mails and posting to Facebook or Twitter once a person passes. One company is even toying with a service that tweets just like a specific person after they are gone. The field got a boost last week when the plot of a British show "Black Mirror" featured similar tools, inspiring an article by The Guardian.

"It really allows you to be creative and literally extend the personality you had while alive in death," said James Norris, founder of DeadSocial. "It allows you to be able to say those final goodbyes."

DeadSocial covers all the post-death social media options, scheduling public Facebook posts, tweets and even LinkedIn posts to go out after someone has died. The free service will publish the text, video or audio messages directly from that person's social media accounts, or it can send a series of scheduled messages in the future, say on an anniversary or a loved one's birthday. For now, all DeadSocial messages will be public, but the company plans to add support for private missives in the future.

DeadSocial's founders consulted with end of life specialists while developing their service. They compare the final result to the physical memory boxes sometimes created by terminally ill parents for their children. The boxes are filled with sentimental objects and memorabilia they want to share.

"It's not physical, but there are unseen treasures that can be released over time," Norris said of the posthumous digital messages.

Among the early beta users, Norris observed that younger participants were more likely to make jokes around their own deaths, while people who were slightly older created messages more sincere and emotional. He's considered the potential for abuse but thinks the public nature of messages will be a deterrent. The site also requires members to pick a trusted executor, and there is a limit of six messages per week.

"I don't think that somebody would continually be negative and troll from the afterlife," Norris said optimistically. "Nobody really wants to be remembered as a horrible person."

The UK-based startup will only guarantee messages scheduled for the next 100 years, but in theory you can schedule them for 400 years, should your descendants be able receive Facebook messages on their Google corneas. The company has only tested DeadSocial with a group of beta members, but it will finally launch the service for the public at the South by Southwest festival in March. Fittingly, the event will take place at the Museum of the Weird.

For those interested in sending more personal messages -- confessions of love, apologies, "I told you so," a map to buried treasure -- there's If I Die. This company will also post a public Facebook message when you die (the message goes up when at least three of your appointed trustees tell the service you've died), but it can also send out private messages to specific people over Facebook or via e-mail.

Though If I Die has attracted a number of terminally ill members, the company's founders think it could be appeal to a much wider audience.

The Israeli site launched in 2011 and already has 200,000 users. Most have opted to leave sentimental goodbyes, and written messages are more common than videos, according the company. So far, the service is entirely free, but it plans to launch premium paid options in the future.

When people sign up, the service will monitor their Twitter habits and patterns to learn what types of content they like and, in the future, possibly even learn to mimic their syntax. The tool will collect data and start populating a shadow Twitter account with a daily tweet that the algorithm determines match the person's habits and interests. They can help train it with feedback and by favoriting tweets.

The people behind the project warn against expecting Twitter feeds fully powered by artificial intelligence, or worrying about Skynet, any time soon.

"People seem to think there's a button you can press, and we're going to raise all these people from the dead," joked Bedwood, who has seen a huge spike in interest in the project over the past week. "People have a real faith in what technology can do."

When a friend of mine died, his wife kept his Facebook page. He was very social and had more than 200 friends in his list on Facebook (mostly due to the business he was in).

So, when his birthday came half a year later, lot's of his Facebook buddies, being unaware of his death, started sending him congratulations and wishes of long life and great health...This was one of the saddest and weirdest moments I had ever experienced online. He was my best friend so it was quite painful to read those messages.

I deactivated my account shortly after that. The reasons were many, but this incident served as a push to quit.